<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button class='btn'>点击修改图片</button>
    <button class='btn1'>点击向box中添加内容</button>
    <div id="app">
        <img src="../img/logo.png" alt="logo" title="logo图标" class="pic" />
    </div>
    <div class='box'>box</div>
</body>
<script src="../js/demo4.js"></script>

</html>